A guiding principle of the proposed research is that coordinated behavior is dependent on the integrated operation of specialized neural structures. Initial work in this area focused on the hypothesis that the cerebellum operates as an internal timing system. More recent psychological and neurological evidence has identified other components such as spatia planning (cortical processing) and temporal coupling (unknown subcortical locus). The proposed experiments provide a programmatic examination of the processes involved in timing and temporal coupling. The specific goals are threefold: The first set of studies will further extend our knowledge of human timing using a new method for partitioning variability related to a timing mechanism and variability that is independent of such a mechanism. The second set of studies focus on temporal coupling, exploring a multiple timer model in which the cerebellum is hypothesized to constitute an array of multiple interval-based timing mechanisms, rather thana single internal clock or oscillator. A key idea in this model is that, while timing reflects a ubiquitous property of cerebellar function, the exact circuits within the cerebellum will vary from task to task. A corollary of this hypothesis is that independent circuits may provide the temporal representations required when performing multi-effector movements or judging two perceptual signals. This hypothesis may have important implications for recent neuroimaging work suggesting a cerebellar role in non-motor tasks. It is hypothesized that cerebellar activation in many of these studies may reflect the preparation of (the timing for) multiple responses. The third goal of this proposal is to explore this idea in two neuroimaging studies. As a whole, the proposed studies should provide important insights into the psychological and neural mechanisms of coordinated behavior. This functional analysis is essential for understanding the functional relationship between cortical and subcortical structures of the central nervous system.